Cation-π Interactions Contribute to Hydrophobic Humic Acid Removal for the Control of Hydraulically Irreversible Membrane Fouling

Fe3+ addition as a promising strategy to enhance the pollutant removal performance and mitigate the membrane fouling of a laboratory-scale membrane bioreactor treating sulfamethoxazole wastewater

Membrane bioreactor (MBR) is a water treatment process combining membrane technologies with activated sludge, which is beneficial to the removal of antibiotics. However, with the extension of the operation cycle, its efficiency in treating antibiotic wastewater decreases and the membrane fouling intensifies. As the presence of Fe3+ could improve pollutants removal, microbial activity and sludge properties, it was anticipated that the addition of Fe3+ in MBR might promote the removal of antibiotics and reduce membrane fouling. The effects of Fe3+ concentration on the removal of sulfamethoxazole (SMX) and membrane fouling were investigated in this work. The results revealed that the removal efficiencies of COD, TN, and SMX was 98%, 86%, and 70%, respectively, when 40 mg/L Fe3+ was introduced into MBR with the influent SMX concentration of 1 mg/L. This performance was superior to that observed in the absence of Fe3+, which was 93%, 74%, and 53% for COD, TN, and SMX removal, respectively. Correspondingly, the membrane fouling rate decreased from 2.52 kPa/d to 1.03 kPa/d, demonstrating that Fe3+ could mitigate membrane fouling. The exploration into membrane fouling mechanism demonstrated that the flocculation of activated sludge was enhanced and the protein (PN) content in the cake layer was significantly reduced. Concurrently, the repulsive energy barrier (XDLVO) between foulants and membrane surface was markedly increased. The study identified four SMX degradation pathways, i.e., N-S bond breaking, C-S bond breaking, N-O bond breaking, and benzene ring deamination. The toxicity levels of the degradation intermediates were determined to span from harmless to toxic as compared with SMX itself. This study offers new insights into the enhanced elimination of SMX through the MBR-Fe process and elucidates the mechanisms involved in mitigating membrane fouling, highlighting the potential of this process in degrading antibiotic wastewater.

Designing Effective Antimicrobial Agents: Structural Insights into the Antibiofilm Activity of Ionic Liquids

Research concerning biofilm control is critical due to the pervasive and resilient nature of biofilms, which pose significant challenges across the industrial, environmental, and healthcare sectors. Traditional antimicrobial treatments are often ineffective against these robust structures. Here, we explore the antimicrobial properties of ionic liquids (ILs) and their efficacy in biofilm disruption. By examining the structural variations of ILs, we highlight the key role of hydrophobicity, noting that longer alkyl side chains in IL cations enhance biofilm disruption and bacterial death. However, upon reaching a certain optimal chain length─usually C12 to C14─the antimicrobial activity of ILs starts to decrease. Furthermore, the symmetry and size of anions significantly impact biofilm elimination. This Perspective addresses a critical gap in biofilm research, revealing the structure-activity relationships of ILs and providing a foundation for designing more effective biofilm-disrupting agents.

Adsorptive chito-beads for control of membrane fouling

Chitosan has excellent antimicrobial, adsorption, heavy metal removal, and adhesion properties, making it a good substitute for microplastic-based cleaners. Here, chitosan microbeads (chito-beads) of various sizes ranging from 32 μm to 283 μm were prepared via emulsion using a liquid on oil method and the feasibility of using them as an essential constituent in a chemical cleaning solution for a reverse-osmosis (RO) membrane-fouling-control process was assessed. Prior to the assessment the cleaning efficiency of a solution containing chito-beads, the interaction energy between chitosan and a representative organic foulant (humic acid (HA)) in a RO membrane fouling was analyzed using colloidal atomic force microscopy, and the strongest attraction between chitosan and HA was observed in an aqueous solution. When comparing the membrane cleaning efficiency of cleaning solutions with and without chito-beads, smaller chito-beads (32 μm and 70 μm) were found to have higher cleaning efficiency. Applications of chito-beads to the membrane cleaning process can enhance the cleaning efficiency through the physicochemical interaction with organic foulants. This study can widen the use of chito-beads as an additive to membrane chemical cleaning solutions to control membrane fouling in other membrane processes as well.

A peptide of PilZ domain-containing protein controls wastewater-treatment-membrane biofouling by inducing bacterial attachment

Membrane-based wastewater reclamation is used to mitigate water scarcity; however, irreversible biofouling is an elusive problem that hinders the efficiency of a forward-osmosis (FO) membrane-based process, and the protein responsible for fouling is unknown. Herein, we identified fouling proteins by analyzing the microbiome and proteome of wastewater extracellular polymeric substances responsible for strong irreversible FO-membrane fouling. The IGLSSLPR peptide of a PilZ domain-containing protein was found to recruit bacterial attachment when immobilized on the membrane surface while suppressing it when dissolved, in a similar manner to the Arg-Gly-Asp (RGD) peptide in mammalian cell cultures. Bacteria adhere to IGLSSLPR and poly-l-lysine-coated membranes with similar energies and exhibit water fluxes that decline similarly, which is ascribable to interaction as strong as electrostatic interactions in the peptide-coated membranes. We conclude that IGLSSLPR is the key domain responsible for membrane fouling and can be used to develop antifouling technology against bacteria, which is similar to the current usage of RGD peptide in mammalian cell cultures.